The present invention relates to a reforming catalyst for hydrocarbons, and in particular to a steam reforming catalyst for hydrocarbons for the improvement of steam reforming catalyst in oil refinery and steam reforming catalyst for fuel cell by providing longer life through suppression of carbon deposition and by effectively utilizing catalytic components, particularly, noble metal components.
The steam reforming for hydrocarbons is a method to manufacture gas consisting of hydrogen and carbon oxides by bringing hydrocarbon and steam in contact with a catalyst. As the typical steam reforming catalysts known in the past, there are alumina type carrier containing alkaline metal oxide, alkaline earth metal oxide and silica, supporting nickel, iron, cobalt, platinum, rhodium, ruthenium, palladium, etc. (Japanese Provisional Patent Publication No. 50-126005 and Japanese Provisional Patent Publication No. 61-280554).
It has been also reported that the catalysts having nickel, cobalt or ruthenium supported on zirconia carrier have also excellent characteristics as the catalyst of this type (Japanese Patent Publication No. 43-12410; T. Igarashi et al.: "Steam Reforming Reaction of n-Butane on Rh/ZrO.sub.2 "; 58th Catalyst Symposium (A), 4B12, pp. 176-177, etc.).
There is also a more recent report, describing that zirconia supporting rhodium exhibits excellent performance in steam reforming reactions for hydrocarbon. (T. Ohtaka et al.: "n-Butane-Steam Reaction on Rh/ZrO.sub.2 Catalyst added with a Third Component; 62nd Catalyst Symposium, 3B305, pp. 118-119.).
Additionally disclosed is a noble metal catalyst supported on a surface layer of a catalyst carrier such as alumina, silica, zirconia, etc. (Japanese Provisional Patent Publication No. 53-78735 and Japanese Provisional Patent Publication No. 48-53980).
On the other hand, steam reforming catalyst have been widely used for industrial application in the reforming of petroleum and petroleum distillate, etc. It has been proposed recently to use a fuel cell with hydrocarbon as the raw material instead of the so-called fuel gas containing hydrogen or hydrogen and carbon monoxide by furnishing a steam reforming catalyst within fuel cell (Japanese Provisional Patent Publication No. 61-260554).
The conventional catalyst of alumina supporting nickel, cobalt, etc. can be successfully used for steam reforing of gaseous or light paraffin when the steam/carbon (i.e., carbon in the raw material hydrocarbon) mol ratio (S/C) is small, however the catalyst is inadequate because coking occurs when the raw material contains a large quantity of unsaturated hydrocarbon such as olefin or the raw material has a relatively large molecular weight such as when heavy hydrocarbons are used. When coking occurs, differential pressure of the catalyst bed increases and reaction efficiency is decreased, finally blocking the catalyst bed. For this reason, coking could be suppressed by increasing the steam/carbon ratio, however there arises the problem that excess steam is required for reaction.
Also, the increase of differential pressure of catalyst bed raises the load of the system. If catalyst bed is blocked, catalyst must be replaced or regenerated. This leads to temporary suspension of the reaction, and more complicated apparatus is needed if catalyst is to be replaced or regenerated without stopping the reaction. Above all, in the internal reforming type fuel cell, the replacement or the regeneration of catalyst means more difficulties, and it is desirable to suppress the coking of catalyst as practical as possible.
It is naturally preferable that the reaction efficiency in steam reforming is high, and the efficiency of the cell itself is an important key for the practical application of fuel cell. Thus, high efficiency of steam reforming of the catalyst furnished in fuel cell is very important.
The first object of the present invention is to offer a steam reforming catalyst for hydrocarbons with excellent mechanical strength, causing no coking and providing longer life of catalyst.
The second object of the invention is to offer a steam reforming catalyst for a fuel cell with high steam reforming efficiency and with no coking.
Further, the third object of the invention is to offer a steam reforming catalyst for hydrocarbons for effective utilization of the catalyst metal and a method for manufacturing the same.